PHOTOS BY BRAD JAKUBOWSKI, DOANE COLLEGE.
For many years, sports turf managers have reaped the benefits of late-season fertilization. Some took the time to research the matter and understand why loading up on nutrition in late fall helps the fields so much, others are happy to just go with the flow and do what everybody else does. No matter which camp you find yourself in, this article will delve into the benefits, timing, products and related cultural practices associated with fall fertilization. Read on to find out if your current protocol can be modified to improve the grasses you manage.
The nature of cool-season grasses
Spending some time in a rhizotron (a special root observation chamber sometimes affectionately known as a “million-dollar hole in the ground”) can be insightful, especially when it comes to late-season fertilization. Seeing is believing, and seeing the results of side-by-side comparative studies involving different nutrients applied at various times provides the observer with a good first look at what happens when nutrients are applied to cool-season grasses in late fall.
Much of the rationale and effect from late-season applied nutrients stem from the cyclical nature of cool-season turfgrasses used for sports turf – perennial ryegrass, Kentucky bluegrass, turf-type tall fescue and creeping bentgrass. These grasses grow well in spring and fall, when temperatures are routinely in the 60s, 70s and lower 80s. Under these conditions, they produce an abundance of shoots and roots, which help to sustain the turf in periods of poor growing conditions such as summer heat stress.
Nutrients applied during the times of conducive growth enhance the expansion of the shoots and roots, creating healthier sports fields. Depending on the mowing height and species of turf, it’s common for the roots of a field to grow to a depth of 6 to 12 inches in spring and fall, but slough off to less than an inch in the heat of summer.
In discussions with coaches, you’ve no doubt heard mention of the importance of timing. Usually these chats involve players who were just a second or two late to make a block, block a punt or catch a pass. Timing is equally important for the sports field manager, especially when it comes to pest control, irrigation or fertilization.
Early and late fall are good timing targets, acting as a one-two punch for the nutritional needs of the turf. Early fall applications stimulate both top growth and root growth, but less top growth than an equal amount of applied product would encourage in the spring. Coupled with cooler weather, these applications help fields recover from heat stress and pest damage that frequently occurs in summer. In Kentucky bluegrass fields, the greatest rhizome growth occurs in fall; applied nutrients encourage recovery and increase the density of the stand.
Advantages of Late-Season Fertilization
- Lengthens the late-fall and winter green period
- Provides opportunity to expand the root system without causing a surge in top growth
- Enhances the rate of spring green-up without stimulating excessive shoot growth
- Reduces incidence of leaf spot and melting out in spring as opposed to early spring applications
- Allows plants to maintain higher carbohydrate levels, encouraging growth of underground structures such as roots and rhizomes.
- Increases winter stress tolerance
On medium to high-maintenance fields, late-season programs do not eliminate the need for spring fertilization, but allow the sports turf manager the opportunity to use lighter rates that result in uniform shoot and root growth. On low-maintenance fields, the importance of late-season fertilization becomes especially important. On these sites, if the maintenance schedule calls for only one fertilization application per year, it is wise to apply it in the late growing season.
What to apply
On occasion, turf has been called a “nitrogen hog,” meaning, as opposed to other plants and crops, it requires relatively high amounts of nitrogen to grow well and responds favorably when those applications have been made. It’s incumbent on the sports turf manager to apply the right nutrients at the right time in the right amount in order to meet the needs of the field without causing damage to the environment.
In late fall, sports fields benefit from applications of nitrogen and potassium. Though usually thought of as a nutrient exclusively to promote top growth, nitrogen satisfies requirements throughout the turf plant, including rooting, flowering, lateral spread, disease resistance and drought tolerance. However, when abundant amounts of nitrogen are applied at the wrong time of year, undesirable results may occur such as increased susceptibility to foliar diseases and excessive succulence.
Take advantage of optimal growing conditions with late-season fertilization.
In general, sports turfs favorably respond to equal amounts of nitrogen and potassium in late fall. The potassium component encourages increased stress tolerance in the turf plants, increasing the likelihood that they will survive extreme winter weather conditions. On fields where more than one application of fertilizer will be made per growing season, 1.5 pounds per 1,000 square feet per year of both nutrients is a reasonable amount.
After late-season fertilization applications have been made, it’s important to wash the product off the blades and into the thatch. A light irrigation should be sufficient. This is recommended for two reasons. First, removing the fertilizer pellets from the leaf blades greatly reduces the chance of foliar burn, which may be more pronounced in late fall than at other times of the year. Secondly, the sooner the product can be moved into the thatch, the better. The thatch layer will act as a temporary binding agent, which will reduce the potential for off-field movement.
A note of precaution
Be sure to use slow-release fertilizers for late-season applications. Research studies at various universities have shown that because the turf is absorbing nutrients at a slower rate than in early fall, the potential for leaching of the applied nutrients is increased. In one study with urea (46-0-0), over 40 percent of the available nitrogen leached out of the rootzone. When this occurs, the fate of the applied nutrients is to make their way to underground or surface water systems, causing pollution. Apply controlled-release fertilizers that release nitrogen via soil moisture, such as sulfur-coated urea (SCU) and isobutydine diurea (IBDU), and avoid microbially dependent sources such as urea formaldehyde (UF), complex methylene ureas (MU) and organics. Temperatures at this time of year are too cold for the latter sources to be of any benefit.
Additionally, do not apply any fertilizer product after the rootzone has become frozen or a majority of the shoots have turned brown. Applications made after this point, no matter the source or composition, are likely to be lost due to leaching, surface runoff or both.
All fertilizer applications should be made with seasonal field use in mind. Football fields will require fertilizer throughout the entire playing season, which includes applying into November as the fields are being put to bed for the winter. Even though plant uptake of nutrients is slowed, carbohydrates are still being accumulated into the plant and can continue into December and even January. Soccer, baseball and softball may normally play into September or October, which provides an opportunity to take advantage of applying it to more actively growing turf. If you make an application in late September or early October, an additional application at the beginning of November can still be beneficial.
Tight budgetary considerations may require treating your target areas as fields within a field. For example, for football, fertilizing a little more heavily between the hash marks with some grass seed may be an option. For soccer or field hockey, the goalmouths may be the target of additional fertilizer.
The take-home message is this: late-fall fertilization provides both aesthetic and physiologic benefits to your turf and provides a head start to the following spring and summer season. Do it while you can!